Mechanical systems frequently employ a cam to convert rotary motion into linear motion. A typical system uses a cam as a rotary input element and a cam follower is used to provide linear output. The cam follower is kept in contact with the cam's perimeter, and the cam having a perimeter that is eccentric with its axis of rotation, will cause the cam follower to reciprocate as the cam is rotated.
The cam, providing the input motion in such a system, is often attached directly to a motor shaft. However, there exists many applications where the cam cannot be mounted directly to the motor shaft because of space constraints, or in other instances wherein the cam follower is required to be placed at a distance from the motor. In these applications, provisions must be made to transfer the motor's rotation to the cam without interfering with the cam follower.
Many applications utilizing a cam require the cam to be rotated incrementally. In applications where the cam is incrementally driven, the rotation of the cam must be controlled to prevent over-travel and subsequent mispositioning of the cam follower. These applications will often use an encoder on the driving motor, or an encoder assembled to the cam to provide the feedback necessary to control the cam's rotation. In systems where the cam is not attached to the motor, the encoder must be assembled to the cam to eliminate the backlash in the drive train (belt, gear, etc.) between the motor and the cam. For example, an angle of rotation is detected on a steering column by attaching a cam to the column (driving mechanism) and further attaching a sleeve having reflective and non-reflective patterns to the cam. A sensor detects the sleeve's pattern for determining an angle of rotation. The interface of the sleeve to the cam can introduce error due to mechanical tolerances and backlash. In addition the sleeve has to be treated (made of two materials, painted, etched, etc.) to provide the differing reflective surfaces, and still further the sleeve represents an additional part introduced into the assembly process.
What is needed is a method and apparatus to integrate the driver element for the cam and the cam's encoder, and directly detect the rotational position of the driver element. This improvement would eliminate a separate encoder, as well as overcoming the undesired backlash and free play that can result in inaccurate cam rotation.